1. Field of the Invention
The present invention relates to a coin identification device for identifying the kind of a coin in an automatic vending machine or the like, and more particularly to a novel coin identification device which uses a magnetic impedance element and which is capable of distinguishing the projections or depressions of a surface design of the coin in addition to the material, thickness and diameter of the coin, which are hitherto distinguishable by the conventional coin identification device.
2. Description of Related Art
The conventional coin identification device is configured to identify a coin by means of a so-called eddy-current magnetic sensor. In the eddy-current magnetic sensor, an alternating current is made to flow to a coil which is connected to an oscillation circuit, thereby generating an alternating magnetic field, which is then applied to the coin. In this instance, an eddy current is produced in the coin by electromagnetic induction, causing a change in the magnetic field. As a result, the impedance of the coil changes to cause a change in amplitude or frequency of the oscillation circuit, so that the change in the magnetic field can be detected. Data about the material, thickness and diameter of the coil is obtained from the detection output thus obtained from the oscillation circuit and is used for the identification of the kind of the coin. The coil is either an air-core coil or a coil having a magnetic core made of a ferrite material and is disposed either on one side or both sides of a path along which the coin moves.
Coin identification devices are used mainly for automatic vending machines for vending tickets, cooling drinks, cigarettes, etc. However, the number of cases where some foreign coins are erroneously recognized by the automatic vending machines has recently increased. As mentioned above, the kind of a coin is discriminated from other kinds on the basis of data of material, thickness and diameter of the coil obtained from the detection output of the eddy-current magnetic sensor. However, some of foreign coins closely resemble some of domestic coins in material and in outside dimension. Such a foreign coin is apt to be mistaken for a domestic coin and allowed to pass the coin identification device. Therefore, it has become necessary to more accurately discriminate similar coins by adding a new function to the conventional coin identifying method.
To meet this requirement, it is conceivable as a new identifying method to distinguish the presence or absence and/or size of projections or depressions of a surface design carved on an obverse or reverse of the coin. However, in order to distinguish the projections or depressions of the surface design of the coin or the stepped edges of the coin by using the conventional eddy-current magnetic sensor, the diameter of a magnetic field spot to be applied to the coin must be reduced to a diameter measuring several millimeters. However, the reduction in the range of the magnetic field to be applied causes the area where an eddy current is produced to become smaller. The change in the magnetic field expected then also becomes smaller accordingly. As a result, it becomes impossible to obtain an adequate S/N (signal-to-noise ratio) of the detection output.